An ignition system that uses a technique capable of restraining radiation of noise caused by discharge of a spark plug in the ignition system. The ignition system includes a spark plug and a power supply section. The spark plug is attached to an engine head. The power supply section has a battery having a ground terminal, and an ignition coil which transforms a voltage of the battery and supplies a transformed voltage to the spark plug. In the ignition system, a metallic shell of the spark plug is fixed to the engine head while being electrically insulated from the engine head through an insulator; an electrically conductive path is connected to the metallic shell; and the electrically conductive path is electrically connected to the ground terminal of the battery while being electrically insulated from the engine head.

An ignition apparatus includes an ignition plug, a boost transformer, an ignition power source and a measurement unit. The ignition plug has a center electrode and a ground electrode. The boost transformer supplies the ignition plug with electric power generated in a secondary coil upon supply of AC power from the ignition power source to a primary coil. The measurement unit measures the discharge voltage of the ignition plug. The ignition power source includes a discharge state determining unit that determines the discharge state of the ignition plug based on the measured discharge voltage and a current controlling unit that controls electric current supplied to the primary coil. When a discharge path formed between the center and ground electrodes of the ignition plug is determined by the discharge state determining unit as being in an over-extended state, the current controlling unit reduces the electric current supplied to the primary coil.

An ignition apparatus includes an ignition plug, a boost transformer, an ignition power source and a measurement unit. The ignition plug has a center electrode and a ground electrode. The boost transformer supplies the ignition plug with electric power generated in a secondary coil upon supply of AC power from the ignition power source to a primary coil. The measurement unit measures the discharge voltage of the ignition plug. The ignition power source includes a discharge state determining unit that determines the discharge state of the ignition plug based on the measured discharge voltage and a current controlling unit that controls electric current supplied to the primary coil. When a discharge path formed between the center and ground electrodes of the ignition plug is determined by the discharge state determining unit as being in an over-extended state, the current controlling unit reduces the electric current supplied to the primary coil.

An igniter includes a switch element and a switch control apparatus. An ignition signal IGT is input to an input line of the switch control apparatus. A high-frequency filter removes high-frequency noise from the input line. A voltage comparator compares an output voltage V.sub.FIL of the high-frequency filter with a reference voltage V.sub.REF, so as to generate a judgment signal S.sub.DET. A driving stage controls an on/off switching operation of the switch element according to the judgment signal S.sub.DET. An off-state dead-time circuit prohibits the switch element from turning off during a predetermined dead time after the judgment signal S.sub.DET transits to a negated level that corresponds to the off state of the switch element.

An igniter includes a switch element and a switch control apparatus. An ignition signal IGT is input to an input line of the switch control apparatus. A high-frequency filter removes high-frequency noise from the input line. A voltage comparator compares an output voltage V.sub.FIL of the high-frequency filter with a reference voltage V.sub.REF, so as to generate a judgment signal S.sub.DET. A driving stage controls an on/off switching operation of the switch element according to the judgment signal S.sub.DET. An off-state dead-time circuit prohibits the switch element from turning off during a predetermined dead time after the judgment signal S.sub.DET transits to a negated level that corresponds to the off state of the switch element.

An ionization detector that reduces the filtering effects of the ignition coil inductances by shorting an inductance of a primary winding of the ignition coil. The ionization detector includes a bias voltage source and an inductance control switch. The bias voltage source supplies electric voltage across an electric gap of a spark plug for detecting ionization within the combustion chamber. The inductance control switch is electrically parallel with a primary winding of an ignition coil and is operable to short an inductance of the primary winding.

An ionization detector that reduces the filtering effects of the ignition coil inductances by shorting an inductance of a primary winding of the ignition coil. The ionization detector includes a bias voltage source and an inductance control switch. The bias voltage source supplies electric voltage across an electric gap of a spark plug for detecting ionization within the combustion chamber. The inductance control switch is electrically parallel with a primary winding of an ignition coil and is operable to short an inductance of the primary winding.

A corona ignition system including a corona igniter, switches, and a programmable controller capable of rapidly adjusting to changes in resonant frequency is provided. Energy at a drive frequency and an output current is provided to the corona igniter. Switches provide energy to the corona igniter at the drive frequency and are activated at different times. The controller obtains the output current provided to the corona igniter, typically once every half cycle, and activates the first switch a predetermined amount of time after a first zero crossing of the output current, wherein the first zero crossing is a zero crossing of the most recent full cycle of the output current. The second switch is activated a predetermined amount of time after a second zero crossing occurring after the first zero crossing. The delay of the system is accounted for by the controller, rather than other components.

A corona ignition system including a corona igniter, switches, and a programmable controller capable of rapidly adjusting to changes in resonant frequency is provided. Energy at a drive frequency and an output current is provided to the corona igniter. Switches provide energy to the corona igniter at the drive frequency and are activated at different times. The controller obtains the output current provided to the corona igniter, typically once every half cycle, and activates the first switch a predetermined amount of time after a first zero crossing of the output current, wherein the first zero crossing is a zero crossing of the most recent full cycle of the output current. The second switch is activated a predetermined amount of time after a second zero crossing occurring after the first zero crossing. The delay of the system is accounted for by the controller, rather than other components.

A method for actuating a spark plug, in which the spark plug is assigned a first ignition coil and second ignition coil. Triggered by a start signal, the primary winding of the first ignition coil is charged, and the primary winding of the second ignition coil is charged with a delay D, for which 0D, by supplying a direct current, wherein, while each primary winding, is charged, the respective secondary winding is blocked; the primary current supplied to the primary windings is measured; after a period T, the primary winding of the first ignition coil is discharged, and with the delay D the primary winding of the second ignition coil is discharged; the secondary current flowing through the spark plug is measured; thereafter the primary windings of the first and second ignition coil start to be charged alternately when the secondary current falls below a threshold; the primary windings are discharged alternately when the primary current reaches an upper threshold; the above steps are repeated until the duration of discharge between two electrodes of the spark plug 1 reaches a predefined value Z.